Posterior segment inflammatory diseases and proliferative diseases (e.g., uveitis, diabetic retinopathy, proliferative vitreoretinopathy, and macular degeneration) are serious diseases that require long-term medication.
Dexamethasone (DEX) and other anti-inflammatory drugs, antibiotics, antibodies, and the like are commonly used to treat posterior segment eye diseases. Posterior segment eye diseases normally require long-term administration of such a drug. However, it is difficult to continuously deliver the effective dose of drug to the posterior eye segment for a long time.
Specifically, systemic administration requires administration of a large dose of drug, and may cause a complication such as hypertension. Eye drops penetrate poorly into the posterior eye segment due to corneal impermeability and the like. Intravitreal injections must be repeated to maintain the effective (therapeutic) level, and involve the potential risk of serious complications such as infections.
A method that implants a drug in the vitreous body (intravitreal implant) is known as a method that can solve these problems, and it has been reported that the intravitreal implant is effective to treat posterior segment eye diseases. However, since the intravitreal implant requires intraocular surgery, infections and the like may occur (i.e., the eye may be significantly affected) in the same manner as in the case of using intravitreal injections.
Periocular drug delivery (e.g., a method that implants a drug in the sclera (intrascleral implant)) is also known as a method for delivering a drug to the posterior eye segment in a sustained manner. This method is safer than the intravitreal implant, but has a problem in that the drug does not sufficiently reach the retina. This is because the drug must pass through a barrier such as the sclera, the choroid, and the retinal pigment epithelium in order to reach the retina, and is eliminated from ocular tissue through the scleral and choroidal blood flows.
The inventor developed technology that implants a drug in the choroid (intrachoroidal implant) (that had been considered to be impossible), and a method for adjusting the drug release level from an intrachoroidal implant, and reported that the intrachoroidal implant is effective for delivering a drug to the posterior eye segment in a sustained manner (see U.S. Pat. No. 8,349,005 and US-A-2014/0221904).
The choroid is situated between the sclera and the retina. Since the retina is an important tissue that includes photoreceptor cells, bipolar cells, ganglion cells, Müller cells, and the like, it is necessary to pay careful attention so as not to damage the retina when performing choroidal surgery. However, since the human choroid is a thin membrane having a thickness of about 0.3 mm, and the intraocular pressure is applied to the choroid in the outward direction, it is very difficult to perform surgery that forms an implant insertion pocket in the choroid without damaging the retina.
The inventor succeeded in placing an implant in the choroid by liquefying the vitreous gel in the eyeball, exposing the choroid, aspirating the vitreous humor to decrease the intravitreous pressure (intraocular pressure), incising the choroid in the tangential direction, expanding the choroid through bleeding to form a space, and forming a pocket in the choroid.
According to this method, since it is unnecessary to perform intraocular surgery, it is possible to ensure safety as compared with the intravitreal implant. Moreover, since the implant is situated close to the retina, the drug easily reaches the retina as compared with the intrascleral implant.